The Flow Cytometry Shared Resource [FCSR] was established in 1979 to support basic and clinical cancer research. The FCSR operates, maintains, and upgrades instrumentation for flow cytometic analysis and cell sorting. Investigators prepare cells and bring them to the FCSR for analysis or cell sorting and pay a fee for the services. These fees are used to partially offset operating expenses. The FCSR operates 3 analyzers and 4 cell sorters, the only ones on campus that are available at all times to all Cancer Institute members. Operating, maintaining, and staffing such a sorting facility is an expensive undertaking best done in a multiuser shared resource setting. Three ofthe cell sorters are 3 laser instruments (one has two lasers) that provide state of the art multiparameter cell sorting of up to 12 simultaneous fluorochromes. In addition to cell sorting, acquiring, analyzing, archiving, and preparing flow data for publication, the FSCR provides consultation, technical advice, collaboration, and maintains a library to disseminate technical information to potential users. The FCSR staff has experience in most all areas of flow cytometric analysis and cell sorting applications and has helped investigators develop a variety of new applications. Staff members recommend assays, help to develop and troubleshoot new protocols, participate actively in the data analysis, and, in general, work closely with investigators to fine tune their individual experiments. An important part of the mission of the FCSR is the education of customers to insure that all users get the most out of the state of the art technical resources. We also participate in the ongoing education of graduate students, post-docs, and MDs. Another important function is to help investigators evaluate existing cell separation technologies before choosing flow cytometry. Thus, the FCSR staff works to help investigators at all levels of experience and expertise to solve problems, not simply operate flow cytometers.